Synthesis of the Alkaloids and Laurifonine Using a Chloroformate-madiated Ring Expansion

Abstract

A convenient synthesis of the reduced dibenz[d,f]azonine ring system is described affording laurifonine in 29% overall yield frm hmveratrylamine.lhe alkaloid laurifine is also accessible in 15% overall yield (as the oxalate salt) by the same route, which employs a methyl chloroformate-induced ring expansion of an erythrinan-3-one derivative.The dibenz[d,f]azonine alkaloidsi and related derivatives2 have attracted considerable synthetic attention.Amongst the alkaloids, routes to protostephanine3-7, erybidine8.9, laurifoninel01l , laurifinell lz6, laurifininell , neodihydrothebaine24, and bractazonineZ4 have been described.There is still a need for further convenient syntheses of these alkaloids and derivatives, which are of chemical, biosyntheticl2113.~4, and pha~ologica15s14 interest.We now wish to report a direct synthesis of laurifonine ( 7 ) and of laurifine (9) which mi~loys a methyl chloroformateinduced ring expansion of an erythrinan-3-one derivative29.The synthesis starts from the readily available hmveratrylamine and y-butyrolactone which rnay 17.18.19and